Abstract
Behavior of an invertebrate, Isonychia japonica, was investigated based on their response to approach flow velocity. Without refugia, the behavior has been categorized into four, walking or crawling, passive walking (or no walking), washout and enduring behavior. The critical depth-averaged velocity for no walking is 0.20 m/s and for washout is 0.40 m/s for the specie. The corresponding local velocity calculated from PIV analysis at the invertebrate height for no walking and washout is 0.12 and 0.22 m/s, respectively. The blocks were placed as refugia for the invertebrates and were successful in providing refugia to the invertebrates. With blocks as refugia, washout behavior was not observed. The local velocity around invertebrate habitat after placement of blocks was reduced to less than 0.10m/s during high flow conditions which is less than the critical velocity conditions without refugia.
